As opposed to having a weak plugin API where all progress depends on the tiny internal team.

The latter suffers more than the first if popularity wanes.

In Atom's case, its lunch was eaten by VSCode which was similar but just better. Based on web tech but with better performance and just as powerful of a plugin API. It wasn't the fact that they let people implement plugins that killed Atom, and they would have been in an even worse situation had they not had a good plugin API.